In recent years, the response of living tissues and cells to various forms of electrical stimulation has been fairly extensively investigated. Out of this work have evolved a number of proposals for promoting the healing of bone fractures and the like, including both invasive treatments involving the use of implanted electrodes and non-invasive techniques utilizing electrostatic and electromagnetic fields.
According to one proposal disclosed in U.S. Pat. No. 3,745,995, metal splints are affixed to a broken bone by screws, and pickup coils have terminals connected both to the splints and to electrodes invasively inserted into the bone. A coil surrounding the limb having the fracture induces in the pickup coils an alternating current signal at a frequency below 1000 Hz, preferably between 1 or 10 Hz and 40 hz, and having gentle, gradual slopes, e.g., a current in the form of a sine wave or a triangular wave. Because this technique is complex and invasive in nature, it is not satisfactory.
Subsequently, U.S. Pat. No. 3,893,462 was granted to Manning for method and apparatus for promoting bone healing by stimulation with an undulating signal having a wave form whose rise time differs from its fall time, the signal being applied by electrodes in contact with the skin of a living body or by coils positioned adjacent the body. It is claimed that this produces in the body a current flow which is of greater magnitude in one direction than in the opposite direction and which enhances and speeds up the repair mechanisms with faster rates of recovery.
In another technique described in U.S. Pat. No. 4,105,017, the treatment involves subjecting living cells or tissues to pulsing electromagnetic fields generated by energizing coils with complex electrical wave forms of a specific frequency-amplitude relation.